Beyond the limit

Answer 1 may well be true and clear, but Answer 2 is the usual expression, emphasising even more plainly that Suzanne is 'beyond her comfort zone' with her existing worries and can't reasonably be expected to handle any more.

One might also talk about any other 'container', or piece of clothing, being 'big enough': the car is big enough to carry a whole family and its luggage; someone's jacket is big enough to be worn over a sweater, etc.; and perhaps a bit more metaphorically, a teenager is 'big enough' to look after themself when out alone in a public place.

'Enough' usually follows its adjective, don't forget.

' ... for to ... ' is wrong and eliminates the odd-numbered Answers (1 & 3); Answer 2 would have worked acceptably if worded as 'too unfit', but people probably wouldn't say that, because 'not fit enough' approaches the imaginary cut-off line in a hopeful attitude from 'below' (i.e., with a bit more luck / effort / physiotherapy, Yogl might be able to climb above the line and reach the required fitness level), rather than squashing down in a rather blameful way from above ('Here's the line and you haven't reached it'). This distinction is as much about the psychology (and tact) of the situation, rather than the wording; rather like dismissing someone as 'too poor' ~ instead of just 'not wealthy enough' ~ to aspire to something.

Answer 2 is the phrase that was adopted.
Answer 1 is just about possible (linguistically) ... but, surely, unacceptably demeaning as a criticism of a human being facing probably one of the most sustained painful experiences that anyone can.
Answer 3 is mis-constructed (see earlier comments), and Answer 4, while it again works well and even has quite a neat linguistic ring to it, clearly falls foul of the same criticism as Answer 1.
'Posh' is a somewhat slangy but widely-recognised word to refer to people or things that are of good quality and perhaps even rather too good, to the extent of being (perhaps deliberately) pretentious ~ such as clothing, vehicles, houses etc. (things that people with plenty of money can choose to buy in good-quality versions as 'status symbols').
It is said to have come from the way that cabins were allocated on ships in the days before most people travelled abroad by air. If they were going from Britain to (say) India, the Far East or Australia / New Zealand, those who could afford to would book a cabin on the 'port' side of the ship on the way out (the left-hand side looking forwards, so mostly facing north away from the sun) and 'starboard' (the other way round) for their return voyage. This arrangement ~ 'Port Outbound, Starboard Home' ~ was abbreviated to POSH, which also conveniently sounds like a piece of plummy-mouthed upper-class slang. (It's usually pronounced 'posh' to rhyme with 'wash', as you might expect; but sometimes it undergoes a further level of satirical exaggeration to be pronounced 'poash', almost more like the French 'gauche'.)
Meanwhile ~ in one further linguistic twist ~ you may be amused to read (truly, we believe!) of a young TEFL learner who had come across the word Posh and its history, and proudly told someone else that it stood for 'Port out, SKATEboard home'!
Anyway, make what you like of the finished phrase in our actual Question, but we hope you can at least 'see where it comes from' culturally!

When we say someone 'oughtn't to have too much trouble' doing something, we mean that we believe that the task ahead of them lies within their reasonable capacity (i.e. it won't be 'beyond them').
The even-numbered Answers 2 and 4 are wrong because votes are countable (obviously enough, if you think about it!), so 'too much' is the wrong way to quantify them. Answer 3 is more-or-less inside-out, and, if anything, suggests a whiff of electoral corruption. ('Too many votes' sounds like a claim of getting '115%' of the total electorate!)

You could perhaps draw your own 'number line' (say, 0 - 18) and decide, in mathematical fashion, where the cut-off points are for these two life phases. The doll phase might run up to (perhaps) about the age of 10, and the reasonably-serious-boyfriend phase begin a few years later (say, 15), so the girl in question might happen to be aged 12 or so.
Apologies to any readers who may find either the outline or detail of this example faintly old-fashioned and/or sexist; but we feel it makes a fair illustration. As current British law stands, a 17-year-old would be old enough to be married (with parental consent) and even to be a parent already (the age of sexual consent being 16) and also a driver, yet not old enough to vote in elections, buy alcohol or legally watch '18'-rated material onscreen. You could practise these language structures within quite an interesting discussion of these seeming anomalies, and with reference to different ages in your own country!

' ... Enough (of) + noun + to + verb' is the construction here; there does not need to be a 'for' as well, as some other languages might suggest. Similarly with adjectives: 'Old enough to fend for himself'.
Usually in such circumstances it will be 'to + verb' or 'for + noun' (or in this case, both, since the verb 'fend' happens to be almost reflexive in its sense and structure):
' ... Quick enough to cross the road ; quick enough for everyone's safety.'

Even an absolute judgment like 'too close', 'too big' etc. can be modified by 'a bit', 'slightly' etc. ~ gently emphasising that there is an excess, even if only a small one:
'The porridge was slightly too salty for my taste'; 'The new foreman seems a bit too big for his boots' (i.e. he is arrogant, assuming more authority than he actually has or deserves).

Only Answer 4 makes clear sense here.