Snakes are escape artists. Piling weight onto the top of her fish tank in the hope that she won't eventually escape is not a good idea. Ditto the "clips" - they work for a while, but under enough pressure they can pop off.

If your snake is 11 months old and she can already push up on the mesh top of the tank then she needs an upgrade before she hurts herself. I would suggest setting up an adult-size tub for her, just give her lots of fake plants and hides to clutter it up.
Both WalMart and Home Depot carry a 100-gal tub that's dimensionally a "40 breeder", with handles on all four sides that hold the top on securely, and it's under $20. Add a heat pad, move over your thermostat from the tank, and call it done.