Just be careful that you’re both designating each other as a beneficiary on any insurance, 401K/other retirement vehicles, or other assets (stocks, bonds, housing, accounts etc). If she’s not legally your spouse, she’s not going to be automatically entitled to any assets if she’s widowed or vice versa.

You both may also want to have a will or power of attorney clause given to each other in case of medical issues which prevent someone from communicating their own will. Family members get the right to act on behalf of their family, but they can’t do anything to help or protect if they’re not legally related in some way. Some places have clauses for common law spouses, but not all do, and not for all circumstances.