A great idea. I've a background adjacent to retreat and wellness breaks and, if you pick well, you could end up with a very lovely experience. What you don't want is someone trying to just up-sell their Airbnb or barn conversion by adding a silent walk, a smudge stick, friendship bracelets and some 'readings'.
Look around at what is available within your agreed travel range and dates, and pick out aspects you think might suit your age group, mobility needs, level of involvement / flexibility, and general vibe and focus (creative expression, meditation, movement such as dance, yoga or somatics, women's circle, skills share, nature / pagan curious, new age-leaning spiritually such as crystals or divination, or connection and sharing), and then shortlist.
Invariably, what you 'get' out of the experience will stand in direct relation to your openness to participate, learn and share, so, providing you choose well and let yourself lean in to the weekend, it could be really enriching.
Also, it seems your friend might be one step ahead of you in terms of enthusiasm -it's nice for her to feel like she can get into whatever you choose to attend fully without worrying that her companion (you) may think that she's being silly, or over the top (if activities engage on an emotional level), depending on what the content offers, so try to find a retreat where you can match her level of curiosity and enthusiasm.
Have a lovely time!