What is she like when she is awake? Is she active & responding to things? Are you concerned during the day when she is up?
I think the heat drains them as I see it with my kids. Someday I could quite easy curl & for a nap if given the chance.
Make sure she is not too hot when asleep & if her longer sleep in affecting day sleeps to much then you could get her back into the routine if you are concerned about that.
She may be going through a growth spurt & needing more sleep...maybe saving energy for getting ready to walk

could be lots of normal reasons.
There is always something to worry about when being a parent.
If concerned see a Dr or ring health-line.