Manager a bitch best way to handle it

Manager being a complete a hole ever since being on maternity leave meant to get paid this Friday I’m down to half a tub of formula and I’ve been told not to ‘rely’ on my smp this Friday as she may not pay us until the Monday as this is technically our payment day but For the past four years of me working for her she’s always paid on the Friday and paying Monday would mean breaking my contract as it states fortnightly and Monday would be over a fortnight xxxx does anyone else think this is wrong ?xx