I would just reply "No thank you we don't need any supplies, I am sure the girls can make do with what we have" And maybe reassure her that the girls will playing in the house or close in the yard.
On a positive note I'll mention that my BF and I are very different in our parenting styles and our kids have successful play dates and sleepovers every week. We compromise and respect each others rules and ideals which is the key. One example: My children are not allowed in a pool with out an adult there at all times, she on the other hand, is comfortable with her kids in the pool adult-free when her DD13 is poolside, I am not. So when my kids are over she accommodates my swimming rule. And I accomodate her no trampoline rule when her kids are at my house.
Getting know someone takes time, this lady may be a heli-mom but she may also just be uncomfortable with a new situation, give her a chance this awkward phase may pass.
