Hmm . . . interesting. Yes, she was very unpopular, and I would say she mostly suffered from comparison with the well-beolved Queen Astrid. The people said to Leopold, "Sire, we thought you had your face turned towards us in mourning. Instead you had it hidden in the shoulder of a woman."
Also, as Leopold's popularity decreased during and after WWII, so did hers by association.
Besides that she had a way with intrigues,and tryed to influence the (in the early fifties)still very young King Baudouin,she more or less took over the role of "First Lady",until Boudewijn married Fabiola.
Upto then both Leopold and Lilian lived at Laeken as was Boudewijn,but as there was,in a very early stage,tension rising between the two Ladies,they were more or less "forced"to move out,and Lilian took along what she could in terms of fe art,furniture and...jewelry.Lilian de Rethy didn't miss a single event in order to glitz and glam till then,she revelled in it.
Moreover she was a controle freak towards her children,that eventually alienated them from her.And to her dispair and frustration,all three married "commoners"instead of members of,preferably, Reigning Houses.As they say,there's something good in every person,it still is hard to get around Lilian de Réthy,néé Baels,in order to find exactly that.History sofar doesn't judge favorably towards her.She now rests in the Royal crypt in Laeken,next to both Leopold and Queen Astrid.She finally is among Royalty,but not quite as she intended.
Btw,the tomb of Queen Astrid is still adorned with flowers,the late Queen is still revered,as is King Baudouin,as his tomb too carries a huge heart of roses(at least it the last time I was there)from Queen Fabiola.