They own the property jointly so she may have to apply to Court for an order for sale. Whether the Court will grant it depends on the judge's assessment of the evidence & circumstances. If she simply sues him for her share she may get a judgement in her favour but be unable to get the money out of him unless he either sells the property or has other funds to pay it.
She really needs some legal advice before starting any Court claim.
She also needs to try to determine what % of the equity she is claiming. If the property is owned as tenants in common this will be specified on the title document, but if it is owned as joint tenants the starting point is normally a 50:50 split. However this can be varied by taking account of the amount each party has contributed to the cost.