Although there are many free cemetery records available online, sometimes you need to use a subscription website. Although I found a memorial on Find a Grave for Louisa Mulder (nee House), there was no image. I was unable to find a memorial for her on BillionGraves. I therefore had a look for her on the Victoria, Australia, Cemetery Records and Headstone Transcriptions, 1844-1997 collection on Ancestry, as they have transcriptions from the Melbourne General Cemetery, (they also have transcriptions from Boroondara Cemetery (Kew), St Kilda Cemetery, Footscray Cemetery, Coburg Cemetery and Lilydale Cemetery) to see if there was any additional information.
I was able to find the transcription of the headstone:
In affectionate remembrance of Louisa mother of Thomas MULDER who departed this life 28 Dec 1878, age 46 yrs also Thomas Alexander MULDER eldest son of the above died 3 Feb 1922, age 68 years also Elizabeth MULDER beloved wife of the above died 4 Aug 1932, age 77 years
I was then able to find the memorial for her son Thomas on BillionGraves, which included an image of the headstone. There is probably no memorial for Louisa on BillionGraves because the details for her are quite faded on the headstone.
Find My Past has a similar collection Victoria Cemeteries, but when I looked for an entry for Louisa Mulder, there was no entry. It appears that their collection does not include the Melbourne General Cemetery.