A great gift idea for your girlfriend who loves How I Met Your Mother could be a merchandise from the show, such as:
1. How I Met Your Mother DVD Box Set - this includes all of the seasons of the show for her to re-watch and enjoy anytime.
2. HIMYM themed coffee mug - get her a mug with a quote or image from the show on it to use during her morning coffee.
3. Legendary T-shirt - get her a shirt with Barney's signature line "Legendary" printed on it.
4. HIMYM Wall Art - look for wall art inspired by the show, like a poster of the gang at MacLarens or a quote from her favorite character.
5. Bro Code Book - you could get her a copy of Barney's Bro Code that she can read and laugh at the funny rules.
6. HIMYM board game - there is a How I Met Your Mother board game called Suit Up! that you could get her to play with friends and family.
Hope this helps!
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