Something lovely to do in Birmingham!

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I really want to treat a special lady (my godmother) to a lovely day out - she's been amazing this year as I had a baby last July and has simply been a rock (I don't have much family of my own)
She is from Birmingham and I live about an hour away - I want to whisk her off and do something lovely that stretches past lunch out that she will remember.
I have toyed with taking her to London for afternoon tea but it will be a long day for her and not sure really worth the effort (she's nearly 70) as I'm not local I have no idea what lovely things there are to do and was hoping to get some Inspiration? Happy to travel around the midlands for the right thing? Thanks in advance!!

Afternoon tea at the Botanical Gardens, maybe? Or go to the Botanical Gardens and then for afternoon tea at the Malmaison or the art gallery in town?

The National Memorial Arboretum in Walsall is lovely.
What kind of thing does she like doing? On a beautiful sunny day I'd prefer to be outside rather than sitting in having lunch.

She's had both of her hips replaced recently so anything too physical is a bit of a no go! The botanical gardens is a great idea - not sure how good the afternoon tea is though? Looked on the website and it doesn't say much and was keen for it to be really special... thanks for the suggestions so far - much appreciated x