_hypocaust, 
To regain the Women's Ashes, England need to win the ODIs 3-0 (or 2-0 with a no result/abandonment).
In the last five years, Australia have lost one ODI, bookended by the 1st & 5th longest winning streaks in the format:
26 Aus 2018-21
17 Aus 1997-99
16 Aus 1999-00
16 Ind 2016-17
15 Aus 2022-23*