Hi sorayas mom. I would just like to add to what ydnic said. Personally what I would do on days when she is not settling for her pm nap I would give her maybe 30Min's tops playing in crib, less if you are confident that she is not going to settle at all. Get her up for maybe 30Min's perhaps give a drink and a snack, read story's, something very low key. Then try to get her take her nap. Hopefully she will then be tired enough to take a nap. If you find time is ticking on and you don't want this late pm nap to effect bedtime you can just give a catnap, using the same rule of thumb Ydnic mentioned, if she naps for 30Min's she should be able to do another 2.5-3hrs A time, although at this time of day I would tend to go for a shorter A time.
So I would try this.
1.45 nap time (doesn't sleep just plays)
2.15 out of bed (low key activity)
2.45 nap time (hope she will sleep

)
3.15 wake her
5.45 in crib hopefully asleep by 6pm (nice early night to compensate for reduced nap sleep during the day)
You may have to juggle how long you let her play first nap attempt and how long you keep her up before going back for nap but hopefully you should be able to squeeze in a catnap later on. If she will sleep in pushchair or car, you can even take her out to get to catnap.
IMO if she takes a really good morning nap over her pm nap then I would do all you can to preserve this good am nap. That way when she needs to transition completely you can just push this morning nap later and later until it falls around midday, losing the afternoon catnap on the way. If you start to notice her am nap get shorter I would start to extend her morning A time to get her tired enough to preserve the nap length.