looking good

There's alot more ppl with more knowledge than me on here but from I know there's usually two reasons for that..
1st, she needs repotting. If she's root bound they've got nowhere to go but up

or..

she may be getting a bit over watered.. the roots drowning further down in the soil and they're trying to breathe. but she looks pretty mint so my guess is a repot.

Hope this helps.. cheers