My condolences for the loss of your partner.
I had an Ashbory bass. Just sold it today to someone in UK after playing it for a few months.
It was a really lovely instrument, and my first bass instrument. I was a complete beginner to bass when I got it. It was a challenge, but not overly difficult.
I would've loved to keep it, but I only sold it because finances were very tight and I have a bass guitar coming my way.
To start off, you can use it as an accompanying instrument by simply playing chords. In bass, the "chords" are simply the notes on the strings. Don't need to bother with Minors, Majors, 7-chords, etc for now. If you have chords for a song, just play the single notes on the bass. I suppose it takes some familiarisation with the bass guitar tuning.
The Ashbory is a great little instrument. I got it because I think the Ubass is a bit overpriced.
If you haven't already, consider replacing the white, silicone strings to the same strings that the Ubass uses (the black polyurethane strings from Road Toad Music). They are MUCH better than the default strings. Last longer and feel less sticky to play.
The fretless nature does take more getting used to as far as playing with good intonation goes. You have to estimate where you press your fingers, as the fretlines that are inlayed do not match up perfectly with tuning.
And also consider changing the battery by unscrewing the back panel. The default batteries that come with it are cheapo "heavy duty" batteries. Alkaline batteries use a lot better.