5 month old napping too late and too long

[FretfulPiglet]

Any advice would be really appreciated: My DD has been napping fairly well in the day (3/4 x; almost textbook times) and bath/bedtime around 7pm (which fits well with DS aged 3) until this last week, when she has started catnapping in the day (up to 45mins 2/3 times a day) and then going down for a 3.5 hour nap around 5pm, waking to be fed at 9pm. She then needs feeding around 1am and 5am - previously she was feeding at around midnight and 6am which suited us all much better.
Do you think she is trying to drop a nap? Or should we be trying to keep her up a bit longer and bath her at say 5.30pm (not very practical with demanding toddler)? Or ...?

I would try lengthening morning and lunchtime naps past catnap length into 'proper nap' length. The pm massive nap suggests not enough sleep through the daytime.

5 months is a usual transition time when moving from several short, frequent catnaps though the day to 2 or 3 longer naps. At 5 months my DD would have a 2 hour morning nap and a 2 hour afternoon nap. Depending on the timing of the afternoon nap, would sometimes additionally have a 30 minute powernap at around 5.30. Previous to 5 months she was sleeping around 45 minutes in every 2 to 2 1/2 hours through the daytime.

Thanks FATEdestiny. I'll definitely aim to extend her naps, which used to be longer. Currently she wakes up after one cycle and starts squealing so I get her up; I'll try and let her get back to sleep if I can!