I think you are asking about three separate issues
- Until what age can one see one's daughter nude?
- Can one pray in front of naked child?
- Can one pray near a toilet/potty?
You are welcome to edit your question if somehow you wanted to ask for different things. Briefly,
1. Until what age can one see one's daughter nude?
I don't believe there is an issue for a mother to see her daughter nude but don't have sources handy. There is no issue of Yichud (being secluded alone) between a father/daughter or mother/son (SA Even HaEzer Siman 22:1) although I am pretty sure it is not appropriate for a father to see his daughter nude past the age of bat mitzva (but don't have sources here). I will edit if others can help with sources.
2. Can one pray in front of a naked child?
From R Jack Abramowitz
One may not discuss Torah or other holy matters in the sight of
genitals, neither his own nor another person’s, even a child’s. (The
one obvious exception is at a brit mila)
Closing one’s eyes is not sufficient so long as it is in front of him;
rather, a person should turn away so that he is no longer facing the
nudity. The Rema rules that in a case of need, we may be lenient when
in sight of the nudity of a boy under nine or a girl under three (OC
Note that turning away, or even moving if needed, is allowed during amida. Speaking however is not allowed. See here for details.
3. Can one pray near a toilet/potty?
You can pray near a toilet/potty which is in a different room, e.g., near a bathroom with an open door but in all cases you must be four amot from the source of foul odors and not see tzo'ah. See here for details. So in your case it appears you can continue to pray if she brings her potty but not if she starts using it.
For practical rulings remember to CYLOR.