I found this website that sells Paris souvenirs, including sweatshirts.
https://www.souvenirparis.com/en/collections/sweat-shirts-souvenirs-paris
This is what they say:
Specializing in Paris souvenirs, the Parici online store offers you a wide range of Paris gifts, textiles and gadgets to offer on the theme of Paris, its monuments, and other typically French tourist places.
Par'ici - 52 rue mouffetard 75005 Paris, FRANCE
We are open 7 days a week from 10 a.m. to 7 p.m.
Tel. +33 (0)1 43 31 79 85
Siret : 398805457 00015
Another thought...Would she be interested in a Sorbonne University sweatshirt? A few years ago, while staying in the Sorbonne area,
I stumbled upon the university gift shop. Of course I bought the sweatshirt and wear it frequently. I regret not getting a tote bag but it's on my to do list for a future trip.
Located at 10 Rue de la Sorbonne, 75005
https://www.google.com/maps/place/Boutique+de+la+Sorbonne+et+des+Universit%C3%A9s+de+Paris/@48.8495128,2.3432928,15z/data=!4m6!3m5!1s0x47e671dd3ef34341:0x355d59ed7e78627e!8m2!3d48.8495128!4d2.3432928!16s%2Fg%2F11c5fzk9x4?entry=ttu&g_ep=EgoyMDI0MTAxNi4wIKXMDSoASAFQAw%3D%3D