First time with my girlfriend

First bikepacking trip (2 days) with my girlfriend this week-end in French Camargue.

We started from Arles, went South to Salin de Giraud the first day. Then West on gravel roads between the sea and the swamps, then North on a gravel road between horses and fighting bulls in the wild. To finish with a bit of rural roads to join Arles.
I highly recommend this ride, the beauty is astonishing.

It was awesome and very beautiful. She liked it a lot. But Im asking myself question about her capabilities for future trips.

We did two days, 40km the first day, almost only cycling roads (ViaRhona). And then 60 to 70% gravel roads the second day.

The first day we rode at almost 20kph with a litle bit of wind facing us. She was happy and found it easy.
But the second day. After 20km of gravel roads, she slow down her pace gradually to the end of the trip. And we had a good tailwind the whole day.
She finished by riding at approximatively 14kph.

As you can see on pictures, her bike is absolutely not optimized for performance.

So Im asking myself, what should I plan for our next adventure. This week it was super flat. But Im afraid she would not be about to ride with ascensions. Even 5m per km.

What are your tough, what mileage and ascent per day do you recommand me to plan for our next trip ? And how much with her actual bike compared if she had a more normal bike ?

Thanks all !