Well the good news is that you will be able to see her once Metro Melbourne enters the Third Step, just not in her home if she has already "bubbled" with another household. You can however meet with her outside of her property: in any public space or at a cafe/restaurant etc.
Third Step
Leave home: no restrictions on reasons to leave home or distance but stay safe
Public gatherings: increased to up to 10 people outdoors (infants under 12 months of age are not included in the cap)
Hospitality: limited indoor and predominantly outdoor seated service, group limit of 10 and density limits, and indoor cap 20 patrons and outdoor cap 50 patrons per venue
Intrastate travel: allowed across Third Step area
Entertainment: outdoor venues and spaces open with density quotients, patron caps and COVIDSafe Plans which must be published online for large spaces.
Accommodation: open, with caps per the household bubble. = So you can stay overnight, but just not at you mums., as she has "bubbled" without you.