You can't make her. Give her a little more time. She is not beyond the age for that development. Don't worry. Her back just needs a little more time to strengthen.
In one day, I got 12 responses! Thank you all so much for your advice, helpful hints and reasurance! I guess I ended up just second guessing myself, if I am encouraging my baby enough to achieve certain milestones. You could call it first-time-mom syndrome. I’ll let you all know how it goes and in the meantime we’ll just have fun! Thank you very much for your time to help me!