FJ if you can get your DH to hold her, you can slip the syringe into the corner of her mouth and squirt it in and at the same time stroke her throat with your hand. Stroking her throat will stimulate her to swallow.

If you are alone with her then wrap her up in a blanket so she can't wack the syringe away with her hand.

I must say I do like the suppository idea. Slip it in when you're doing a nappy change and she'll never know