On 30 October 2017, Fett reached her best singles ranking of world No. 97, and on 21 May 2018, she reached her best doubles ranking of No. 348. Fett has won five singles and four doubles titles on the ITF Women's Circuit.
On the juniors' circuit, Fett had a career-high ranking of No. 12, which she achieved on 24 February 2014. She was the runner-up at the 2014 Australian Open girls' singles event, wherein she fell to Elizaveta Kulichkova in the final.
At the 2017 Hobart International, she qualified for her first entry to the main draw of a WTA tournament. She then lost to eventual champion and fellow qualifier, Elise Mertens.
Later in the year, she reached her second WTA semifinal at the Japan Women's Open, again coming through qualifying, while also scoring her first victory over top-20 player and top seed Kristina Mladenovic. She lost to fellow qualifier Miyu Kato after failing to convert a match point. She made her top-100 debut after this success.
At the 2018 Australian Open, she appeared in the Grand Slam main draw for the first time as a direct entrant. She played in the second round against second-seeded Caroline Wozniacki and had two matchpoints, leading 40/15 at 5–1 in the third set. However, she lost that game and the successive five games to yield the match.
Grand Slam singles performance timeline[]
Key
W
F
SF
QF
#R
RR
Q#
P#
DNQ
A
Z#
PO
G
F-S
SF-B
NMS
P
NH
(W) Won; (F) finalist; (SF) semifinalist; (QF) quarterfinalist; (#R) rounds 4, 3, 2, 1; (RR) round-robin stage; (Q#) qualification round; (P#) preliminary round; (DNQ) did not qualify; (A) absent; (Z#) Davis/Fed Cup Zonal Group (with number indication) or (PO) play-off; (G) gold, (F-S) silver or (SF-B) bronze Olympic/Paralympic medal; a (NMS) downgraded Masters Series/1000 tournament; (P) postponed; (NH) not held. SR=strike rate (events won/competed)
To avoid confusion and double counting, these charts are updated at the conclusion of a tournament or when the player's participation has ended.