airgirl - you'll know when you are really ready!
Contrary to a lot of opinions expressed here, I think you are a good judge of when you are ready to solo. For me,it was when I wanted to get rid of that tyrant in the back seat (glider). I knew I was ready, and the club then had sent a new instructor to fly with me who had never flown with me before, he made me do all the stalls and nasty bits. And then he got out of his seat, said "I'll be watching you, and I want to see you do a couple of stalls and recoveries on your own."
Well, said I to myself, I will do exactly as I please, I will just go up and bimble around and I WILL NOT do any stalls, so there. So I did, and of course no problems at all with the landing. And going home on the M40 I had the most wonderful sense of superiority to all those groundlings in their fancy BMW's.
Landing is something you need to be comfortable with, especially in a glider as you don't have the option of a go-around! So yes, do plenty of practice with an instructor beside you who has promised to intervene only if absolutely necessary, yes, go with someone else than your regular instructor, who may have a certain investment in seeing you achieve solo and may be pushing you out of your comfort zone.
When I was doing my first winch launch solo, the instructor got out of the back seat, I said "I'm not ready to solo yet!" But he got out notwithstanding; the winch died at 300 feet, I dithered, and landed a bit firmly, and the tyre went flat, and that was it for the day. If it really had been my first solo (my flying up till then had all been airtow) my confidence would have been flattened as well.
Since way back then, I have done a LOT of instructing. Women are less confident than men, in general. Men tend to be overconfident.
Just ask the auto insurance companies which gender has the better record!