Leonard says he lost the Batman flash drive years ago. In The Veracity Elasticity (2016), Penny teases Leonard about not even noticing that Batman is no longer on his key ring, but neither of them state it was a flash drive. It may have been a different key chain.
A first rule in giving someone a used laptop is to wipe it's hard drive of all files just in case you don't want your information getting out. While it is possible for Penny to not know or have forgotten this, Leonard would have remembered. So the Bitcoin folder shouldn't have been on that laptop when he gave it to Penny.