As Dzug2 indicates, bona fide gifts (per se) aren't taxable and they can't 'get anyone into trouble'. The only reason that the form asks gifts of over £3000 in any one tax year (during the past 7 years) is that amounts in excess of that can be counted as part of the deceased person's estate when it comes to calculating Inheritance Tax. But if the total value of the estate comes to less than £325,000 there will be no Inheritance Tax to pay anyway.
If the estate does exceed the £325,000 Inheritance Tax threshold, then the whole of any amounts gifted by your mother, in excess of £3000 (to your or to anyone else) during the 3 years prior to your mother's death will count towards the value of the estate. For gifts (in excess of £3000) given between 3 & 4 years prior to your mother's death, 80% of their value is regarded as part of the estate. For gifts (over £3000) in the previous year, only 60% of their value counts towards the estate. For gifts (over £3000) in the two years prior to that, 40% and then 20% of their values respectively count towards the estate.
Probate interviews are very relaxed and informal affairs. Don't worry about yours.
Chris