This is the case I have in mind. I wish to express that impact acted in a way that was severely adverse.
It impacted her severely adversely.
The proposed text above doesn't feel right at all, though.
Learn English – How to modify an adverb with another adverb
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There are a few common idioms or sayings that fit the situation rather well, though they do not mean exactly “having so much [work] because you chose it yourself”.
There’s “You made your bed (– now lie in it/you are going to have to lie in it)”, which means that the person you’re talking to has created their own mess, so now it’s their own responsibility to fix it.
Similarly metaphorical is “You reap what you sow”, which compares the bad situation to a field—if you sow bad seeds, you’ll reap bad grain; likewise, if you ‘sow’ a bad situation for yourself, you’ll have to ‘reap’ the consequences, no better.
More direct and pragmatic, “You asked for it!” is used to indicate that someone should not be complaining about their current situation, since it is only what they themselves asked for in the first place.
Even more direct is “You brought this on yourself”, which does not mince words and simply says that the person addressed caused their own misery themselves.
Note: All of these could be considered somewhat rude—their intention is to be blunt. If you wish to be softer and more polite about it, I don’t think there’s a fixed expression available that fits. Instead, I would just phrase it in a natural, but polite, way; something like, “I’m sorry to hear you’re so caught up in work—but you mustn’t forget that you did ask for quite a heavy workload, so you really only got what you asked for”.
An idiom that is a bit less rude would be Be careful what you wish for—you might get it (or it may come true, or lest it come true; there are several variants), which quite properly warns someone not to want or ask for something without first thinking through what actually getting it will entail.
It could be either one, depending on whether "trying" is a noun (then you use "alleged") or a gerund, which is a verb form (then you use "allegedly"). This is because adverbs can't modify nouns, and adjectives can't modify verbs. The ambiguity of structure arises because "-ing" has multiple uses in English, and here, we might be dealing with the "-ing" that derives nouns from verbs or the "-ing" that accompanies gerunds, which are verbs.
Some English speakers might not accept the adjective "alleged" here, because they could be missing a lexical noun "trying". This is a difference between inflectional endings, like the ending in the gerund (which does not change the part of speech), and the derivational ending in the noun "trying". Derivational forms are not basic to the structure of the language -- individuals may differ in whether they are acquainted with specific words in the lexicon.
What is going on is clarified if we change the example so that "trying" has a direct object, since nouns do not take direct objects:
Alice's trying ice cream had left Bob wary of any gourmet foods she might suggest.
Now, you can't use the adjective "alleged".
Best Answer
Not all adverbs are allowed to modify other adverbs. The adverb severely cannot modify another adverb.
You could correct the sentence by saying "extremely severely" or by saying "it had a severely adverse impact on her".
How do you determine which adverbs can modify other adverbs (or adjectives or verbs, for that matter)? I don't know; I haven't found any lists online, and none of the dictionaries I've checked classify adverbs according to what they are able to modify.