Am I being helpful or up-ending the wedding?

You sound lovely and well intentioned but the last fortnight before a wedding is just far too short notice to be adding social events.
Social events that the bride doesn't have to lift a finger to organise or even attend if she doesn't want to? Nah, that's really silly.

My first thoughts are that your dd is either ashamed of you or ashamed of his parents and family.

It would put me on guard for stopping any more of my money on extras being spent.

I think the reaction indicates something else is going on

Don’t people do wedding rehearsal dinners anymore ?

Lots of people do this now.

It's usually a lovely relaxed day

It doesn't really matter why her daughter objects - if she "became very uspet" becuase a simple offer was made that she was at liberty to refuse, she's being unreasonable. If her mother is pushing at it and inisting she gives "good reasons" not to do it, she isn't being.
She may have met her husband's parents and know that they and hers will loathe one another, for all we know. Maybe she despises them and doesn't want to expose her parents to that. Maybe she doesn't like her mother and knows her inlaws won't either. She's the one with the information, let her make the decision.

You sound lovely and well intentioned but the last fortnight before a wedding is just far too short notice to be adding social events.
The B and G are probably stressed out about getting everything together in time. I know that before my wedding as well as working , confirming final details with the venue, catering, guests, bridal party, hair and makeup was a lot !
Also maybe his family are weird and she doesn’t want you to meet them yet?🙈

I don’t understand how so many people seem unable to comprehend that not all families are local.

Your daugher is being ridiculously dramatic, what exactly is she upset about? Not being able to control everyone's movements in the weeks leading up to and after her wedding?

In inverted commas though. So not literally.

Yes she has. It’s in the Op.

The daughter says she was busy and the events don’t work for her.

If you first made these suggestions this close to the wedding date and requested your DD and her partner’s presence at one or both events I can see why she’d find it stressful - extra stuff to do, she might have other preferences for her wedding weekend.

My mum did similar to this at my wedding, with more notice. Groom’s parents and our own (large, geographically distant) extended family over to hers the evening before the wedding. She had good reasons and motives, but I really didn’t want to do it and found it stressful in the run up and wedding weekend. I didn’t tell her this!

Now DH and his siblings chose not to attend and stuck with our original plans of relaxing at a hotel with our friends!

To be ‘really upset’ over a first world problem shows her immaturity. She needs to use her words and explain why she doesn’t like the idea.
how bloody ungrateful. Her mother has saved for years so she can be a princess for the day (money would be better spent elsewhere IMO)

Oh sorry, did I say it was sinister!? It’s still an odd choice of words, I’d be baffled as to why my mother though a debrief about my wedding was needed the next day. And combined with the daughter being upset, clearly we aren’t getting the full picture here.

Completely this. OP has made a couple of perfectly nice, friendly suggestions.

She hasn't stepped over any boundaries or sone anything wrong and the bride's reaction is just weird.

"...arranged to meet DH's parents as soon as we were engaged."

Why? You weren't marrying his parents. There's no reason you should even like his parents, let alone your relatives.

My mother hosted a party the day after which we were not expected to attend and my mother in law did too which we were expected to attend although we planned to be on our honeymoon. In the end we went to my mother’s party as we needed to return something to her and firmly declined my MIL. I got in trouble for it but we had a great time and I never regretted it nor did DH.

I still don’t understand what your daughter’s objection is though? She must have her reasons. Without you explaining those we can’t comment on whether you or she or neither are being unreasonable. What did she actually say. “I don’t like that idea because…”?

You sound very thoughtful and I think that your daughter is probably caught up in her own plans but her response wasn’t very kind. I am very surprised that they are getting married and you haven’t met his parents. Why hasn’t your daughter already facilitated that?

Sounds like lovely ideas but for reasons unknown she doesn't want you to do it, so shrug it off and just accept it.

Weird yes but nothing to spoil the lead up to the wedding over.

Is there a class issue with the inlaws are they very posh or something and the dd is embarrassed and doesn't want to tell you?

She literally used the word debrief.

Id have loved to have a parent offer this and think it was lovely of you to offer. If she's decided she doesn't want that thats okay but she doesn't need to be dramatic and get upset at the offer.

The drink with the groom’s parents sounds like the most normal thing in the world. Generally I would think the B and G would attend. Are they busy elsewhere? But you can certainly go ahead without them.

My family always have a morning after brunch when we’ve travelled for a wedding. Generally the B and G are excused!

Close enough to attend? Don't you think that most parents will travel a lot further for their offspring's actual wedding than they would just to meet somebody's parents?
I can't imagine where my daughter might get married that I would consider to be too far to attend; but if she does want to get married to someone from China, I doubt I'll be popping over regularly to meet the in-laws beforehand.

I met DD's mother in law before the wedding and we really hit it off and have met a few times since when she is in the area. Thinking of both my DD's who got married locally, the day after the wedding we had family picnics with no expectation for either of the couples to join us but they wanted to hang out with extended family who had travelled a long way to be with us.

When DD and DS were married further from home we made it clear that we did not expect to see them the next day.

"I also offered to host a casual gathering of our relatives the day after the wedding, before guests departed the area, which I thought would be helpful and a lovely way to ‘debrief’ and relax. My daughter was very upset and that I could do as I like, but she will be too busy and these events don’t work for her. Am I in the wrong here?"

Are you going to do as you like and do you see yourself as helpful or up-ending the wedding?