I don't think there is in Ancestry as I think you are referring to a chromosome comparison facility. Ancestry seem adamant about not introducing this.
My Heritage and Gedmatch seem to be the most popular sites for this. I've used both. I think there is also the 'Leeds method' , similar to Painter ?, but I've not used it.
Others might have other recommendations.
Gadget
Add - this is assuming that you can persuade her to give you access to her results.