Any fourstroke would be a bit easier to learn on. I learned on a YZ80 though. I'm 17 now and 5'7'' i was 14 and 5'6'' barely back then. The YZ was fun to learn on because it was smaller, but at 5'8'' I would really suggest a KX/RM100, with a flywheel weight for ease of use in the woods, and also a KTM105SX if you can dish out the cash. The big wheel 80s would work just fine to learn on. The KTM has the largest seat hieght out of them all, I beleive and seems to have more spread-out power. I would sit on a few and find the biggest bike that you feel comfortable on. You would be able to fit on a 125 as I would have been too, but I understand your hesitation on getting one. It must be a girl thing. Lol. Maybe even a 125 fourstroke with the larger wheel combo. Look for, YZ85, TTR125L, RM100, RM85L, DRZ125L, CR85Expert, CRF150/230, KX100, KLX125L, KTM85SX, and KTM105SX. I bet you'd be happiest on a 100+cc two stroke bike. Right between the 80s and 125s power wise, but without the wieght of full-size bikes and fourstrokes. The KTM105SX seems most promising with the spread out power, good for low end, but many people swear by KX100s with a little woods modifications. The 100cc bikes have bigger chasis then the 85cc bigwheel bikes, which only have the larger 19/16in wheel combos. The KX/RM and KTM both have bigger, modified frames so they have a bigger seat hieght then just the bigger 85s. It would probably fit you better height-wise. I would look at manufacters websites and the womens forum on this site for seat heights on the 85s. I believe the KTM and Yamaha are the highest. Agian, see what is in your area and sit on a few, and try them out. You're bound to find something you'll love. Oh, and i almost forgot. Check out the KDX200/220. They are a bit bigger engine wise, but have a seat height a little lower then a 125, and are the easiest two strokes to use the power on. They have a smooth delivery of power, and are the ulitmate woods machine for a begginer. May be a little heavy for you though. Like I said, check some bikes out. Looking at bikes are your best bet, even if youre not sure at first. Dont limit yourself, and have fun!!! Make sure to budget in some gear too!!!!
Dont forget to check out the Women's Forum!!!!!
~Jamie