OP, my mother said pretty much the same to me and a raft of other things that were heinous. Through MNet I now realise she is a classic narcissist.
Only you know your mother's nature to tell if what she said came from a good place.
When DS1 was born I remember holding him in my arms and realising I loved him so much I could never, ever purposefully be unkind to him. That sorrow lasted many weeks but it was the first wake up call that it wasn't me who was "difficult".
In many ways your mother is right. Marriage, or a life long relationship, is hard work even when everything's right. You don't truly know how your partner will react to life's ups and downs until you face them and when you do you have to find a way to support each other.
Children are hard work and very expensive - it was the never having a break from them that I found difficult rather than the physical work but the joy outweighs it. The joy of smelling the head of your very own new born, the first words and watching them become increasingly independent. The pure joy of watching them at a rockpool, as their little hand reaches for yours on the way home. And it carries on all the way to their graduations and beyond.
Along the way are broken hearts (and arms and legs) and in our case a phase of adolescent mh problems (now resolved), notwithstanding a few teenage rows and episodes of sheer terror when one has been out until 2am with no communication.
But the love and the joyous times make up for that.
We have been married for 29 years and the dc are 25 and 22. I wouldn't have had it any other way.
My mother by the way still tries to find fault with all I do and we will never match up to her fantasy of the perfect family.