Invisible Step-Granny

I have been married for 22 years. My husband's ex-wife is also remarried for 22 years to her current husband. I will call her Judee. Judee is unable to restrain herself from intruding when I happen to be at a our grandchildren’s party, ball game etc. She is a bit sly about it all, but she is annoying. For example, (one of many similar situations) We show up at a birthday party. The moment she sees us come in, or the moment we walk over to say hello to the kids, she hovers in the space near us regardless of how large the venue is and then Judee transforms into Grandma Extraordinaire. She starts speaking loudly in a sing song voice, and begins using ridiculous superlatives as she practices soliloquy techniques, and speaks out into the universe near us so that we can hear whatever she is saying. I might be bending down to give the 4-year-old a hug, and in the very near background I hear Judee harping over me interrupting our interaction with something like, "Oh, isn’t she so precious in her lovely sparkling dress, isn't she just gorgeous?" Speaking to no one in particular.
Same party, we decided to leave a bit early and asked if we could let the party girl sit with us in a spot off to the side to open our present for her. My stepdaughter is most agreeable and said, "Sure" We sit down while everyone else is playing and visiting. The moment Judee sees my husband and I sit down with the child, Judee is bounding over, "Oh, is she opening her presents now?" My Stepdaughter says, "No, My Dad and Granny are just letting her open their present." Judee takes a position just above where we are sitting and commentate the entire present opening right down instructing her to tear the paper and to asking the child if she loves it and loudly expressing her opinion to the universe of the "extraordinary" gift.
In addition, we have quit telling my step-daughter when we will be at games, and now we just show up because if she mentions it to her mother in passing, Judee will be there every time doing her best Mary Poppins. She just can't help herself. I am waiting for her to break out in song and dance one day.
Before you chide my husband, we are both at a bit of a lose as to how to make her go away since she is pouring on the nicey nicey, singy songy, with the kids all the while ignoring me, speaking over me, and interrupting any meaningful interaction that I have with the kids.
After trying to ignore her rudeness for years now, I have decided that the next time she hovers and interrupts I am going to stand straight up and say, "Oh my, I am so rude. Did I interrupt yours and Child's conversation or interaction? Excuse me, I will come back when you are finished." I have decided to us my feet to remove myself from the situation. Any helpful suggestion on how to handle a rude interloper who just can't accept that her children and grandchildren actually love me and vice versa. They often come to our house, and all is well and normal when Judee is nowhere to be seen.
It is good just to vent and to put something out on the internet that might help other people as there is a dearth of information about how to handle exes after grandkids come along. She has always ignored me, so this is nothing new. Thank you in advance for helpful kind comments.