Less water retention can also cause feet to become smaller. But, a loss in cartilage would not be a good sign as estrogen should maintain it and a decrease in sex hormones would lead to cartilage loss, as it happens in older people.
Arthritis Rheum. 2000 Sep;43(9):2081-90.
"Transcriptionally functional ER are present in adult articular cartilage, and ERT increases the production of IGFBP-2 and the synthesis of PGs by chondrocytes from surgically menopausal monkeys. These results indicate that estrogen can have a direct effect on adult articular cartilage."
Joint Bone Spine, Volume 70, Issue 4, August 2003, Pages 257–262
"in vivo in ovariectomized rats, estrogen replacement prevented the cartilage breakdown caused by interleukin-1β [60]."
Menopause: September/October 2004 - Volume 11 - Issue 5 - pp 508-518
Suppression of elevated cartilage turnover in postmenopausal women and in ovariectomized rats by estrogen and a selective estrogen-receptor modulator (SERM)