Perhaps she could say, "In lieu of gifts, please consider making a donation to the March of Dimes". If you say please it doesn't sound bossy.
Or maybe a poem...
Our little guy is turning one!
We've planned a day of so much fun.
We're glad that you can come and play,
But let's not forget those who don't have such happy days.
Instead of gifts we'd love to donate lots
To that great charity, Toys for Tots.
Please, instead of a gift for Josh, bring a new, unwrapped toy to be donated to Toys for Tots. Thank you!
(I just came up with the poem off the top of my head, so if someone can improve upon it, please feel free!!)