Thank you for your question.
You were right to notify both you and her insurance companies.
There are three types of "other insurance" clauses.
1- If there is other valid and colectible insurance, this police does not apply = escape clause
2. If there is other valid and collectible insurance, this plice obnly kicks in after the sirst policy is exhausted = secondary clause
3. If there iis other valid and collectible insurance, the polcicies will be applied pro rata = pro rata clause
Pro Rata Policy A has 1,000,000 dollar limit, policy B has 100,000 - pro rata means policy A pays 90% and B pays 10% of the damages.
There are countless permutations on how these are combined in real life. Pro rata vs. secondary, secondary vs. escape, etc.
You can get a frtee consultation from some of the auto insurance attorneys listed by location here.
If your insurer says anyhting other than that you are covered, you may want to consult a local attorney to review policies and determine your options.
You need an attorney to read both policies that apply to your vehicle to determine what your rights are.
I hope this information is helpful.