Yes, they absolutely do (first hand experience!). She may not be a hoarder in the clinical sense, but she’s obviously someone who gets a massive dopamine rush from acquisition and from getting (what she believes is) a bargain.
If she also conversely hates ‘waste’, it leaves her with a constant problem of over accumulation. Too much stuff, and all the guilt, worry, overwhelm and aggro of having to get rid of new or thrifted items you’ve bought but don’t actually want or need, and pressure to clear out stuff you already own in order to create space.
They often have difficulty letting go of things in a way that feels psychologically ok to them, but one of the easiest ways of doing this is to foist it onto family and friends. By presenting your old shite as a lovely gift, it’s very difficult for other people to turn down, and achieves the double whammy of moving stuff on in one easy, guilt-free dump, but also validating your shopping habit. If you can persuade yourself that you’ve bought something with someone else in mind, that they’d find it useful and that you’re only doing it to be kind, then you never have to address your own behaviour. And if someone tries, no matter how nicely, to push back, you can shut it down by being hurt at their ingratitude.
At its root it’s not generosity, it’s selfishness. She wants to carry on buying shit but can only do so indefinitely by forcing other people to facilitate it. The only way to shut it down is to gently but firmly resist it, every time. ‘Thanks mum, but I don’t need it and don’t have room for it, sorry.’ Hold firm, even when the offence and hurt feelings get wheeled out - it’s an easy way of controlling the situation and forcing you to go along with what she wants, but the more you hold the line, the easier it’ll get!