Pony Books: (English language only)

SUMMER WITH PRINCE
aka SOMMAR MED PRINCE (Original Swedish title)
(WAHLSTRÖMS? [SWEDEN] 1982)
Reprinted in the USA in English language by Stabenfeldt/Pony in 2007
SUMMARY: Lisa is bored in her new life in the country. She misses her old friends and her parents don't take her suggestion she go for riding lessons seriously. But then Stella moves next door; an old woman with a secret, and a horse called Prince: the sweetest, most gentle horse in the world Lisa falls in love with Prince and life seems to take a turn for the better. But problems are just around the corner….

Collector's info:
This has been reprinted in Swedish since it was first published and also recently in English language in the USA. Fairly easy to find in the USA (and presumably in Sweden) but quite hard to get hold of elsewhere.