Digging down

[Hermione15]

Ok, so this might be a silly question, but I'm new to this...I got my six year old Hermanns tortoise, Hermione, about a month ago. She was kept on tortoise pellets on a small tortoise table. She is now in a bigger table, with topsoil as substrate, which I know needs to be kept damp below the surface. Under her UV/heat lamp it's 32-33 degrees, dropping to about 21-22 at night when it's off, with the 'cool' end being around low 20s during the day and lower at night (I'm afraid I don't know exactly, but I would say between 15-20- the thermometer is at the 'warm' end).
My question is this- Hermione never digs, instead she just tucks her head into a corner and sleeps, or in her old home she used to try and climb to sleep- is digging a natural instinct that she knows how to do, or does she need to be taught to do it because she's always been on pellets? Maybe she is too hot? There is a lot of topsoil in there for her to bury herself in, but she's displayed no interest whatsoever! She occasionally goes in her hide but mostly just stays in her corner....I am not sure how I could teach her to dig, but if it helped I would give it a shot!!

Thanks for your help! Christine