I recommend taking a look at Franchi. They have two youth models of semi-auto's. The "AL 48" and "620". The AL 48 is long recoil operated and very light and slim. The 620 is gas operated which might kick a little less. It is only slightly heavier and wider than the AL 48. I would also suggest a 20 gauge with a 26" barrel length. They cost around $450.00-$550.00.
My daughters daycare owner was looking for a new shotgun last year. Like yourself she is under 5' tall. I told her to check out the Franchi's. She ended up buying the 620 youth with 26" barrel and she just loves it. He husbands family owns a pheasant fram here in Michigan. So, she uses it for that as well as shooting clays. The Franchi's are one of the best buys out there. I own one of each in 12 gauge and have not had any problems. The have been as reliabile as my Browning's "Auto-5" and "Gold 3 1/2".