just be aware, unless you have an Apple Music family account, you're only allowed one stream at a time.
So if she asks siri to play something, and you're at your house listening to your phone, your stream will stop.
And same for the reverse. you could kill her stream by starting music on your phone.
if she has her own apple account, and apple music ID, obviously this won't apply
and another thing to be aware of, the only way to setup a HomePod is with an iPhone/iPad.
You do it by holding your device next to the HomePod. I'm not sure if you would be able to use a device logged into your account to log the HomePod into her account.
--as an alternative to the homepod, and especially for someone without an iDevice,
Sonos is a great option, and fairly comparable in price (Ikea has a $99 version that's decent, but probably just a bit under the mini in sound quality)
The new Roam is $169, it's sound is at least comparable to a HomePod mini, and it's battery powered, so you can move it around easily (or just leave it on its charging base), and you can also use it as a bluetooth speaker to take with you when you leave the house. in sonos mode it has voice control.
Or their basic speaker is $199 with voice control, $179 without. and it will sound better than a HPmini.
sonos will sign in to pretty much any streaming service, and the music plays directly on the speakers. (be mindful of stream limits if you guys are sharing an account)
You can also sign into an account multiple times, so you can have "my Spotify" and "their Spotify" so you have access to both sets of playlists, and don't have to worry about stopping their streams.
They have controller apps for iOS, Android, Mac, and Windows.
there's no siri, but Alexa or google assistant are available on some models.