If there is a house, investments etc, then I guess it’s quite likely you’ll be paying inheritance tax. From what I remember, you have to settle the tax bill before you can get probate and until you get probate you can’t do anything else.
It may well be that you’ll have to sell the house to clear the inheritance tax bill. You’d also have to get a valuation of the house for inheritance tax purposes, which might clarify things (she won’t be able to buy it cheap from the estate on the QT). Also, you only have 6 months from the end of the month your mother died to pay inheritance tax. If you don’t pay, you start clocking up interest on the tax bill, and that is certainly not in the best interests of the beneficiaries.