Apologies for the length of this but as a life long adorer of persians my heart went out to you and your cat. This is sadly one of the prices to pay for the unique and wonderful persian personality. As Hissy says, they are very sensitive cats who bond very closely to their owners and can be deeply affected by change, and serious toileting issues are one of the two major reasons that persians end up being rehomed when things at home go wrong. They are a high maintenance breed who need a great deal from their owners.
It sounds like your girl is struggling to deal with the baby, possibly with new children in the house with your daycare, and had a very natural reaction to being moved to a new home temporarily. It is very likely that it's going to need real time, effort and committment from you to help her overcome this problem, and it may be you that need to think about whether you can manage that at this time- if not then it's important to start taking action to find her a permanent new home that CAN give her that time and input, before her toileting behaviours are so ingrained that it will prevent her being able to settle with new owners. Someone is going to have to make that committment to help her overcome this if it's behaviour rather than health based; just moving to a new home won't fix it. The problem will go too.
If the vet is sure she is healthy, there's several things you can try. It might be well worth confining her in one room that's very easy to clean so you're less worried, and making that room a safe space for her where the baby never goes. Offer several litter boxes, just as the experts here recommend- a minimum of three (two for her plus at least one for the other cat) but at first even more might help- add several comfortable perches, and make it really easy for her to be 'good'. If you spend time with her in there, feed her in there and make it a sanctuary, and things between you get more positive because you're not constantly cleaning up after her, then the stress on both of you should settle. When things are better then you can gradually start taking her with you to visit other rooms with the baby. I would make the family room out of bounds to her if that's a trouble spot, long enough for the habit to be broken, and not even think of reintroducing her to that room until her toileting habits are totally re established. It may be that that room will have to be permanently out of bounds to her, persians have long memories!
It might also be worth looking for the largest litter trays you can find: persians aren't always brilliantly co ordinated and need a lot of space to manoever in comfort. If you're going to beat this though her trays must be SPOTLESSLY clean. Most persians are very finicky and if her tray is dirty or smells when she goes to it, you really can't blame her for finding somewhere else to go. Try giving her just enough litter to cover the bottom of the tray, scooping it as often as you can through the day- with some of mine that's been every time the tray was used if I'm home, they ARE that fussy
- and changing the litter every day, as well as wiping out the tray with soapy water if you can't wash it daily. Confined to one calm, safe room with plenty of immaculate trays, you should be able to rebuild good sound toileting habits, and then gradually increase her freedom to whatever extent she can cope with. So long as they have plenty of company, most persians aren't too worried about huge amounts of space: they'd rather be with you than doing anything else.
If you do come to feel that you can't meet her needs, then
try and find a persian rescue centre for advice. They are around, the people who run them are dedicated persian lovers and very experienced in dealing with the specific emotional and behavioural problems of this gorgeous breed. They are usually happy to travel as necessary to collect a cat in need, and will be her best chance for serious help to get her toileting habits re established, and they will see to it that she goes to a very carefully chosen home who are prepared for her needs and will make a success of the placement. It's very important not to mess her around any more than is absolutely necessary by moving her to temporary homes and possible homes and then back again- that runs the risk of disturbing her to the point where she will become unhomeable.
Whatever you decide, best wishes to you both, I hope very much your girl can settle down and overcome her current difficulties.