The truth of the matter is is she needs to evaluate what is best for her.
Are you interested in competition, or your current horses? It will take a lot of training and growing a bond with your 2 year old to get him to the level that you need to be to have the potential you need, and he might be praised in the long-term effects, but if you have a horse that is sooner capable of what you are looking for, you should go for it.
I think that you should go for the lease if you are wanting to show now. During this time you can train with her while you work on your two-year-old and maybe by the time you terminate your lease you can start continuing with the two-year-old, and have more experience to push that young horse to the best of his/her ability.