Souvenir heureux n° 4 ¶
¶
(¶
¶
Quand je me sens mal, ce qui arrive souvent, j'ai une cache de souvenirs heureux qui me rend mieux'aident à me sentir mieux/me soulagent/me redonnent du baume au coeur.

You're repeating an entire verbal phrase here ("se sentir mal"), so the pronoun can only be "ce qui"
All the alternatives at the end would sound natural ("rendre mieux" is a literal translation that doesn't work)

Le prochainsuivant est le numéro quatre.)

the following = le suivant
"le prochain" would work in a sequence (if you had already talked about number three in this text, for instance)

En 2010, je me rends chez ma grand-mère aà Winnipeg (Canada).

-d never ever is a first person singular ending in the indicative

at someone's house = chez

a = has
à = on, at, to (preposition)

Je resteséjourne/descends à l'hôtel et leun matin, je vais dans le lobby'entrée/le hall.

"rester" means "to stay" in the sense "not to move"
"to stay" for a short period of time somewhere is "séjourner" (especially in the case of a hotel or an inn)

I don't know about Canada but in "France French", "un lobby" is an interest group pushing the agenda of a political or economical organization. It's never used about a room

"LE matin" would mean "every morning", but you're talking about a single event here

Là(-bas), il y a une très belle femme dans la trentaine avec son fils à côté d'elle.

I would rather use "là" instead of "là-bas" here. "là-bas" implies something pretty far away from a point of reference earlier in the text. If you just meant "there in the hotel", "là" would be enough

Soudainement, le fils lancenroule les bras/jette les bras autour de la'une des (très longues) jambes de sa mère, comme un aimant.

"enroule" would be more elegant than "jette" IMO
It's of course understandable given the context, but "la très longue jambe" sounds kinda off, as if the woman had only one leg

C'est la chose la plus mignonne que j'aite jamais vue.

j'aie, tu aies, il ait
Accord du COD antéposé => vuE

--« Comme c'est mignon ... »

Direct speech is put in quotation marks and introduced by a colon (a comma and then "dit-elle" or "répond-il" at the end works too)
A hyphen is used to indicate someone else is talking
No space before an ellipsis, one space after

Elle dit, ¶
-- Il le : « Il fait toujours n'ça, où qu'on aille/peu importe où on va. »

Je dis, ¶
--réponds : « Eh bien ... il aime sa maman. »

"répondre" is more accurate and fitting here