This company seems to have a good range of thicker mats...
http://www.needlesports.com/acatalog/Mail_Order_Camping_Mats_54.htmlI am sure that at 3 months gone she is needing the loo a lot so maybe a sheewee (sp?) so she doesn't have to get up and down for a wee in the night would help too. I think you can get them with bags that turn the urine to gel and don't smell.
Make sure she has a good pillow, and as COTW said one for under her knee when she gets a bit bigger. I'm sure she will be fine - have fun!
BTW I wild camped at 7 months fine but 8 months was my limit - I had to go home after a few hours. Do I still qualify for a medal?